Rebase on kubernetes v1.6

Add plugin management subcommands for installing and removing plugins
to `$HELM_HOST/plugins`.

Install accepts a vcs url or a local directory.

```
$ helm plugin install http://github.com/adamreese/helm-env
Installed plugin: env

$ helm plugin list
NAME    	VERSION	DESCRIPTION
env     	0.1.0  	Print out the helm environment.

$ helm plugin remove env
Removed plugin: env
```

closes #1977

There was a bug in SemVer 1.2.2 that miscalculated a couple of
comparison patterns.

A few bugs were fixed in ghodss/yaml since the last update.

Closes #2087

Possible fix for #1639

Closes #1744

There was a hyphen range bug in semver that prevented constraints
in the form of v2.3.5-20161202202307-sha.e8fc5e5. This would be
parsed incorrectly as a hyphen range and then fail. The bug in
semver was fixed in semver v1.2.2 for this issue.

This adds shasum, int, and float64 functions, and fixes quote escaping
for 'quote'.

Closes #1524

This adds a hidden 'helm doc' command that generates documentation out
of the Helm help text.

Currently it can create:

- man pages for HELM(1)
- Markdown documentation
- bash autocompletions

Those are the three built-ins for Cobra.

The command is hidden so that it doesn't show up to the regular user,
since this is really a specialized task. It has the advantage of making
it trivially easy to install man pages and bash completion at installation time.

A bug in the semver package caused prereleases to be included in
version ranges by default. Prereleases, per the spec, are not
expected to be API compatible with the releases themselves.

The semver package now ignores prereleases when evaluating
constraints when the constraint does not contain a prerelease. If
the constraint contains a prerelease they are evaluated.

- decouple tunnel from kube client
- add context switching for init cmd
- add unit tests for installer and init command
- refactor installer and remove unused code

This removes the last of the requests for gopkg.in/yaml.v2, and
also the struct annotations.

Closes #1192
Closes #1263

This starts with #1211 and does the other updates necessary for
bumping us to Kubernetes 1.4.

This adds support for OpenPGP signatures containing provenance data.
Such information can be used to verify the integrity of a Chart by
testing that its file hash, metadata, and images are correct.

This first PR does not contain all of the tooling necessary for
end-to-end chart integrity. It contains just the library.

See #983

We need this specifically for trimSuffix.

Closes #1071

Closes #1055

Looks like another Go git repo got moved around.